1. Field of the Invention
The present invention relates to a brushless DC motor, and more particularly, to a system and method for controlling the torque and speed of the brushless motor.
2. Description of the Prior Art
A typical brushless DC motor includes a stator, including three windings, spaced at 120 degree electrical from one another, for imparting a torque on a rotor. The torque imparted on the rotor causes the rotor to rotate. Those skilled in the art of motors and generators appreciate the efficiency, economy and simplicity of brushless DC motors wherein there is no actual physical contact between the stator windings and the rotor. In order to effectuate the operation of the motor, a properly timed and spaced magnetic field is synthesized in the stator windings which imparts a torque on the rotor and causes the rotor to rotate.
The typical brushless DC motor is permanently configured in one of two basic configurationsxe2x80x94either a wye connection or a delta connection. A motor with windings configured in the delta configuration can operate at a greater speed than the same windings configured in the wye configuration. However, a motor with windings configured in the wye configuration can operate with a greater torque at low speeds than the same windings configured in the delta configuration.
Accordingly, in an application requiring high torque at a low speed, the motor is permanently configured in the wye configuration. Consequently, a conventional brushless motor design requires a compromise between high torque at a low speed and low torque at a high speed.
One application of a brushless DC motor is that of providing a source of motive energy for driving a centrifuge rotor in a centrifuge system. A centrifuge system is a device by which liquid samples may be subjected to centrifugal forces. The sample is carried within the centrifuge rotor, which is mounted to a rotatable drive shaft that is driven by the brushless motor. A centrifuge system using a brushless motor with windings permanently configured in either a delta configuration or a wye configuration is limited by the aforementioned compromise between high torque at a low speed and low torque at a high speed.
There is a need for a system and method for enabling a brushless DC motor to operate with high torque at a low speed for high torque-low speed centrifuge rotors as well as to operate at high speeds at a reduced torque for high speed-low torque centrifuge rotors, thus permitting the use of a wide range of centrifuge rotors.
A high torque/high speed brushless DC motor system for controlling both the speed and torque of the motor includes a rotor and a stator. The stator of the motor includes a first, second and third winding. The system further includes means for configuring the first, second and third windings in a wye connection when the speed of the motor is less than a predetermined value and configuring the windings in a delta connection when the speed of the motor is greater than the predetermined value.
In one aspect of the invention, switching means are included in the motor system for implementing the stator winding connection configuration changes. The switching means of the system can be common to both the wye and delta connection configurations.
A method is also disclosed herein for effectuating the configuration of the brushless DC motor in a wye connection when the speed of the motor is less than the predetermined value and configuring the windings in a delta connection when the speed of the motor is above the predetermined value. The method of the present invention can be further implemented by a storage media containing computer readable program instructions for controlling a processor to control a brushless DC motor in accordance with the methods of the present invention.
It yet another aspect of the invention, a storage media having computer readable program instructions embodied therein for controlling a processor, which in turn, controls a brushless DC motor in accordance with the method of the invention.